High-density disk recording medium and apparatus and method of reproducing data recorded therein

ABSTRACT

The present invention relates to a recording medium such as a CD or a DVD in which data is recorded in high-density, and method and apparatus for reproducing data recorded in the high-density recording medium. According to an embodiment, the data reproducing method according to the present invention converts a high-frequency signal reproduced from the recording medium into a plurality of binary signals through comparing the reproduced signal with two or more slicing levels which are different each other, selects one of the plurality of binary signals or a periodic pulse signal based on the difference magnitude between the plurality of binary signals, synchronizes a reference clock with the selected signal, and restores the selected signal into bit stream using the synchronized reference clock.

This application is a Continuation of application Ser. No. 10/635,572filed on Aug. 7, 2003, now U.S. Pat. No. 7,158,463, which is adivisional of application Ser. No. 09/678,334 filed on Oct. 3, 2000, nowU.S. Pat. No. 6,633,527 issued on Oct. 14, 2003 and for which priorityis claimed under 35 U.S.C. § 120; and this application claims priorityof Application No. 99-42931 filed in Korea on Oct. 5, 1999. The entirecontents of each of these applications are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disk recording medium such as acompact disk (CD) or a digital versatile disk (DVD) in which data isrecorded in high-density, and method and apparatus for reproducing datarecorded in the high-density disk recording medium.

2. Description of the Related Art

FIG. 1 is a partial block diagram of a conventional optical disk devicefor reproducing data from a disk. The disk device of FIG. 1 comprises anoptical pickup 2 for detecting recorded signals from an optical disk 1such as a CD or a DVD, a signal detector 3 for yielding a reproduced RFsignal through adding the signal components detected from the disk 1, acomparator 4 for converting the reproduced RF signal into a binarysignal through triggering the RF signal with a reference zero level, aphase lock loop 5 (PLL) for synchronizing an internal reference clockwith the binary signal, a bit stream generator 6 for generating a bitstream according to level and its length of the binary signal using thesynchronized reference clock, and a demodulator 7 for restoring originaldigital data from the bit stream through correcting error, if any, witherror correction code contained in the bit stream.

The conventional data reproducing operation conducted by the opticaldevice of FIG. 1 is described.

The optical pickup 2 makes a laser beam be incident onto mark or pittrains formed along a track of a recording surface of the disk 1 asshown in FIG. 2, and converts the reflected beam from the beam spot intoan electrical signal. The beam reflected from a mark or a pit isconverted into a low-level electrical signal, whereas the reflected onefrom a space between marks or pits is converted into a high-levelsignal.

The components of the converted electrical signal are added in thesignal detector 3 and then results in a RF reproduced signal which isapplied to the comparator 4. The comparator 4 converts the RF reproducedsignal into a binary signal which has only two levels through triggeringthe RF signal above and below a reference slicing level, and applies thebinary signal to the PLL 5 which synchronizes an internal referenceclock with the binary signal in phase. For example, the PLL 5 adjuststhe clock speed of a 4.3218 MHz internal reference clock to have thefalling edge of the internal clock coincided with that of the reproducedbinary signal if the disk 1 is a compact disk. Then, the PLL 5 appliesthe synchronized reference clock and the binary signal to the bit streamgenerator 6.

The bit stream generator 6 converts the binary signal corresponding tomarks and spaces formed in the disk 1 into bit stream referring to thesynchronized reference clock, and the demodulator 7 restores the bitstream into original data while correcting the restored data based onthe channel correction code contained in the bit stream.

To be brief, electrical signal components detected from a generaloptical disk by the pickup 2 are added into a reproduced RF signal whichis converted into a binary signal after being compared with a referenceslicing level, and then is converted into a bit stream based on areference clock synchronized with the binary signal in phase.

Therefore, the minimum length of a mark or a pit to be formed in anoptical disk should be long so that a RF curve generated correspondingto the mark or pit might cross the reference slicing level to betriggered without jitter.

In case that an optical disk is a CD for which the reference clock is4.3218 MHz, the minimum length of a pit or a space is specified to threepulses, i.e., 3 T, which corresponds to 0.86677 μm, among relatedcompanies so that an RF curve produced from the shortest pit formed inthe CD might be converted into a bit stream normally.

In the meantime, the related companies are developing a technology toincrease the recording capacity of an optical disk. The technology underdevelopment is to use a blue laser beam of which wavelength is shorterthan that of conventional laser beam, or is to shorten the marginal gap,which is called as ‘pitch’, between two tracks.

However, since the requirement that a RF curve generated correspondingto a minimum-length mark or pit have enough transition duration to crossthe reference slicing level without jitter should be still satisfied,the shortest mark or pit is not inevitably less than 3 T, which putsrestriction on increasing recording capacity of a track.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide apparatus and methodof reproducing data recorded in an optical disk, which compares a RFsignal reproduced from a disk with multistage reference level andconverts the RF signal or self-generated periodic pulse corresponding toa minimum-length mark or pit into bit stream based on the differencebetween binary signals resulted from the comparison, thereby enabling aminimum-length mark or pit to be formed more shortly than a conventionalminimum-length one.

An optical disk according to the present invention records data in theform of marked phase and unmarked phase such that the length of one ormore marked phases or unmarked phases is shorter than a radius of areproducing beam spot.

An apparatus for reproducing data from an optical disk according to thepresent invention, comprises a signal detector converting ahigh-frequency signal reproduced from the disk into a plurality ofbinary signals through comparing the reproduced signal with two or moreslicing levels which are different each other, and outputting one of theplurality of binary signals or a periodic pulse signal based on thedifference magnitude between the plurality of binary signals; and a dataconverter synchronizing a reference clock with the signal from saidsignal detector and restoring the signal from said signal detector intobit stream using the synchronized reference clock.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate the preferred embodiments ofthe invention, and together with the description, serve to explain theprinciples of the present invention.

In the drawings:

FIG. 1 is a partial block diagram of a conventional optical disk devicefor reproducing data from a disk;

FIG. 2 shows an example of recorded mark or pit pattern and waveformsproduced at several points of the apparatus of FIG. 1 when reproducingthe pattern;

FIG. 3 is a partial block diagram of an optical disk device according tothe present invention;

FIG. 4 is a detailed block diagram of the multi-level comparator of theapparatus of FIG. 3; and

FIG. 5 shows an example of recorded mark or pit pattern and waveformsproduced at several points of the apparatus of FIG. 3 when reproducingthe pattern.

DETAILED DESCRIPTION OF THE PREFFERRED EMBODIMENTS

In order that the invention may be fully understood, preferredembodiments thereof will now be described with reference to theaccompanying drawings.

FIG. 3 is a partial block diagram of an optical disk device according tothe present invention. The disk device of FIG. 3 comprises an opticalpickup 2 for detecting recorded signals from an optical disk 10 havingmarks/pits and/or spaces formed according to the present invention, asignal detector 3 for yielding a reproduced RF signal through adding thesignal components detected from the disk 10, a multi-level comparator 40for converting the reproduced RF signal into two binary signals throughtriggering the RF signal with different reference levels ‘Vref1’ and‘Vref2’, a PLL 5 for synchronizing an internal reference clock with thesignal from the multi-level comparator 40 in phase, a bit streamgenerator 6 for generating bit train according to signal state and itslength of the signal from the multi-level comparator 40 based on thesynchronized reference clock, and a demodulator 7 for restoring originaldigital data from the bit stream through correcting error, if any, witherror correction code contained in the bit stream.

FIG. 4 is a detailed block diagram of the multi-level comparator 40. Themulti-level comparator 40 of FIG. 4 comprises a first internalcomparator 41 converting the reproduced RF signal into a first binarysignal through triggering the RF signal with a reference level ‘Vref1’which is above zero level; a second internal comparator 42 convertingthe reproduced RF signal into a second binary signal through triggeringthe RF signal with another reference level ‘Vref2’ which is below zerolevel; a cyclic pulse generator 43 generating a periodic pulse signalsynchronized with the first binary signal in phase; a signal selector 46for selecting one to output among the first binary signal and theperiodic pulse signal; a logic circuitry 44 outputting a differencesignal between the two binary signals through conducting an exclusive-ORoperation of the two binary signals; and a glitch eliminator 45 passingpulses of the difference signal from the logic circuitry 44 to a signalselector 46 only when the pulse width is broader than a certain range.

FIG. 5 shows an example of recorded mark or pit pattern and a timingdiagram produced from the pattern. The data reproducing method embodyingthe present invention conducted by the optical disk device configured asFIGS. 3 and 4 is described in detail.

The optical pickup 2 makes a laser beam be incident onto mark or pittrains formed along a track of a recording surface of the disk 10 asshown in FIG. 5, and converts the reflected beam from the beam spot intoan electrical signal. The beam reflected from a mark or a pit isconverted into a low-level electrical signal, whereas the reflected onefrom a space between marks or pits is converted into a high-levelsignal.

In the meantime, a minimum-length mark or pit and/or space between markor pit has been formed in the disk 10 such that its length is shorterthan the radius of a reproducing beam spot in order to enhance therecording efficiency of a track. The length shorter than the radius of areproducing beam spot is shorter than 3 T which is the length of theshortest pit or space in a conventional art.

For example, the minimum-length mark has been formed such that itslength is 2 T.

The RF signal reproduced at such-formed minimum-length mark or pit cannot be separated far away from a zero level as shown in ‘A’ of FIG. 5.The reproduced RF signal containing the monotonously-changing curvemarked as ‘A’ which stays around the zero level is applied to both ofthe first and second internal comparators 41 and 42 of the multi-levelcomparator 40.

The first internal comparator 41 compares the applied RF signal with thereference level ‘Vref1’ and converts it into a binary signal which is,in turn, transmitted to the signal selector 46, the logic circuitry 44,and the cyclic pulse generator 43 which is generating a periodic pulseof which level duration is equal to the length of the 2 T mark or pit.The cyclic pulse generator 43 adjusts the speed of the periodic pulse tosynchronize the falling edge of the periodic pulse with that of thebinary signal, and then applies the synchronized periodic pulse toanother input terminal of the signal selector 46.

In the meantime, the second internal comparator 42 compares the appliedRF signal with the reference level ‘Vref2’, converts it into anotherbinary signal, and sends the binary signal to the logic circuitry 44.The logic circuitry 44 conducts an exclusive-OR operation of the twoinputted binary signals to obtain a difference signal which has a highpulse at where the levels of the two binary signals are different eachother, and transmits the difference signal to the glitch eliminator 45.The glitch eliminator 45 blocks a short pulse, that is, glitch of whichduration is shorter than a predetermined time length whereas passing theother long pulse to the signal selector 46.

The signal selector 46 selects and outputs the binary signal from thefirst internal comparator 41 or the periodic pulse signal from thecyclic pulse generator 43 based on whether the level of theglitch-eliminated difference signal from the glitch eliminator 45 ishigh or low.

That is, the signal selector 46 outputs the periodic pulse signal, whichhas short pulse corresponding to 2T mark or pit, from the cyclic pulsegenerator 43 to the PLL 5 while the difference signal is in the state ofhigh level marked ‘b’ in FIG. 5.

The PLL 5 synchronizes the reference clock with the periodic pulsesignal or the binary signal from the first comparator 41 in phase, andthen applies the signal selected at the signal selector 46 to the bitstream generator 6 along with the synchronized reference clock.

The bit stream generator 6 converts the applied signal, which iscombined from a reproduced signal corresponding to marks and spacesformed in the disk 10 and a constructed pulse signal for 2 T mark orpit, into bit stream referring to the synchronized reference clock, andthe demodulator 7 restores the bit stream into original data written inthe disk 10 while correcting the restored data based on the channelcorrection code contained in the bit stream.

As explained above, the mark or pit shorter than 3 T can be restored tooriginal data normally through the operation of the equipped multi-levelcomparator 40 comprising two internal comparators 41 and 42 usingdifferent slicing levels ‘Vref1’ and ‘Vref2’ respectively; a cyclicpulse generator 43 generating a periodic pulse signal whose width isshorter than 3T which is time length of the shortest mark or pit in aconventional art; and a signal selector 46 selecting one from thereproduced binary signal and the periodic pulse signal.

Therefore, the mark or pit can be formed more shortly than conventionalart without data loss in reproduction. In the above embodiment, theminimum-length mark/pit and/or space has 2 T in time length, however,the minimum-length mark/pit and/or space can be more shorter, forexample, 1.5 T, than 2 T without departing from the technicalcharacteristics explained above.

The apparatus and method of reproducing data recorded in an optical diskaccording to the present invention, making it possible to form adistinguishable minimum-length pit or mark more shortly, therebyenhancing the recording capacity of a track formed on an optical disk.

The invention may be embodied in other specific forms without departingfrom the sprit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. A device for processing data recorded on an optical recording medium,comprising: a pick-up unit configured to read or write data from or onthe optical recording medium, the data formed in a marked phase and anunmarked phase, a minimum length of the marked phase or unmarked phasebeing 2T, T being a channel bit clock; and a signal processor comprisinga first A/D converter and a second A/D converter, wherein the first andsecond A/D converters output a first and a second signal respectively,the signals are different each other and the signal processor outputs abinary signal based on the first and second signals.
 2. The device ofclaim 1, wherein a reference level of the first A/D converter isdifferent from that of the second A/D converter.
 3. The device of claim1, wherein the signal processor outputs one of the first and secondsignals by comparing the first and second signals.